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Seattleites may need more vitamin D to optimize immune function
If you want to make sure you are covering all your bases when it comes to flu prevention, there is more you can do than follow the typically-spouted recommendations. In fact, for sun-starved Seattleites, it is especially important to make sure you’re not deficient in Vitamin D, a crucial vitamin for immune system functioning linked to seasonal, epidemic flu.
Vitamin D has profound effects on immunity in addition to its many other functions. It dramatically stimulates the expression of potent substances that kill disease-causing viruses and bacteria known as anti-microbial peptides (Cannell, 2006). These peptides exist in immune cells such as infection-fighting white blood cells and in the outside layer of cells that line the respiratory tract which are the primary cells contacted by flu viruses and other respiratory pathogens.
Vitamin D deficiency, common among Seattleites, is linked to influenza and respiratory tract infections. Studies have shown that children with vitamin D deficiency are predisposed to respiratory infections, especially viral infections rather that bacterial (Walker, 2009). In adults, studies show that higher vitamin D levels in the blood are associated with lower levels of upper respiratory infections (Ginde, 2009).
Vitamin D supplementation has been shown to reduce the incidence of respiratory infections in children, while studies using vitamin D supplementation in adults to prevent infections have been mixed (Cannell, 2006). For example, daily supplementation with 800 IU vitamin D3 for 12 weeks in older people living in the UK and Scotland was associated with fewer self-reported infections and antibiotics, but the estimated 10–15% reduction was not statistically significant (Avenell, 2007). It could be that higher dosages for a longer treatment time would have resulted in statistically significant reductions in infections and antibiotic use in this older, northern-latitude-based population.
Sunlight is an important source of vitamin D, but don’t be fooled into thinking that getting out in the Seattle sun this spring and summer will be sufficient, especially if your Vitamin D levels are already too low. A recent study of 93 people living in Hawaii with high amounts of sun exposure (participants spent an average 22.4 hours per week outside without sunscreen) found that 51% of the subjects had serum 25-hydroxyvitamin D concentrations below 30 ng/mL, defined as "low vitamin D status”. These results implied that the common clinical recommendation to allow sun exposure to the hands and face for 15 minutes may not ensure vitamin D sufficiency, according to the investigators (Binkely, 2007).
Because of our higher number of cloudy days, Seattleites, including children, may require higher doses of vitamin D supplementation to achieve normal vitamin D status, which should be evaluated with laboratory tests for concentrations of serum 25-hydroxyvitamin D. If you haven’t already done so, ask your doctor to check your levels during your next visit. Ideal serum levels are between 30 and 60 ng/mL. Insufficiency is 25 to 30 ng/mL, rickets or osteomalacia is evident at less than 20 ng/mL, and frank insufficiency is less than 10 ng/mL (Wike Malone, 2008).
When a vitamin D supplement is prescribed, 25-hydroxyvitamin D levels should be monitored every 3 months until levels normalize. The goal for adults is to achieve a 25-hydroxyvitamin D level >30-40 ng/mL. For infants and children, according to the American Academy of Pediatrics revised guidelines, serum concentrations of 25-hydroxyvitamin D should be at least 20 ng/mL.
Current research has determined that the daily recommended intake for most adults is 1000 IU. Up to 2000 IU per day is now commonly considered safe for most adults. The American Academy of Pediatrics recently revised intake guidelines, stating that all infants and children, including adolescents, should have a minimal daily intake of 400 IU of vitamin D beginning soon after birth, which is up from the previous 200 IU minimum for children.
Supplementation of vitamin D can be obtained through daily multivitamins in addition to diet. The average daily adult multivitamin contains 400 IU of vitamin D, while children’s formulas contain an average of 200 to 400 IU.
Those with vitamin D deficiency are often treated with a prescription of 50,000 IU once per week for 6 to 8 weeks, with serum levels drawn afterward to ensure an adequate level. Personal experience, both as a patient and as a physician, has shown me that even this may be insufficient to adequately restore levels to optimal.
References
Avenell A, Cook JA, Maclennan GS, Macpherson GC. Vitamin D supplementation to prevent infections: a sub-study of a randomised placebo-controlled trial in older people (RECORD trial, ISRCTN 51647438). Age Ageing. 2007 Sep;36(5):574-7.
Binkley N, Novotny R, Krueger D, Kawahara T, Daida YG, Lensmeyer G, Hollis BW, Drezner MK. Low vitamin D status despite abundant sun exposure. J Clin Endocrinol Metab. 2007 Jun;92(6):2130-5.
Cannell JJ, Vieth R, Umhau JC, Holick MF, Grant WB, Madronich S, Garland CF, Giovannucci E. Epidemic influenza and vitamin D. Epidemiol Infect. 2006 Dec;134(6):1129-40.
Ginde AA, Mansbach JM, Camargo CA. Association Between Serum 25-Hydroxyvitamin D Level and Upper Respiratory Tract Infection in the Third National Health and Nutrition Examination Survey. Arch Intern Med. 2009;169(4):384-390.
Walker VP, Modlin RL. The Vitamin D Connection to Pediatric Infections and Immune Function. Pediatr Res. 2009 Jan 28. [Epub ahead of print]
Wike Malone R, Kessenich C. Vitamin D Deficiency: Implications Across the Lifespan. The Journal for Nurse Practitioners. 2008 June;4(6): 448-454.
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